Electronic trigger circuit



Feb 24, 1948. w. A. MILLER El AL 2,436,482

ELECTRONIC TRIGGER CIRCUIT Filed Dec. 2, 1943 1 +8 +t T13 /Ru 6! EL? INPQT 6? P114 s5 f" INVENTOR IfiuM/MA Musk.

Patented Feb. 24, 1948 ELECTRONIC 'rnrcomt cmourr William A. Miller, Port Jefferson, and Eugene It.

Shenk, Brooklyn, N. Y., asslgnors to Radio Corporation of America, a corporation oi Delaware Application December 2, 1943, Serial No. 512,558

2 Claims. 1

This invention relates to electronic trigger circults.

It is known to employ trigger circuits in the form of a pair of triodeelectrode structures whose grids and anodes are regeneratively coupled. In such known types of trigger circuits, the length of the output pulse is affected by the following factors: (1) The impedance of the tripping circuit, (2) the impedance of the circuit on which the trigger circuit output is impressed, and (3) the interaction of the trigger function of the vacuum tubes with the tripping and output functions.

An object of the present invention is to pro vide an electronic trigger circuit in which the input, output and triggering circuits and functions are isolated from one another.

Another object of the invention-is to provide a trigger circuit employing multi-grid tubes having certain electrodes regeneratively coupled and in which the output is derived from a different electrode than those which enter into the regenerative circuit.

A further object is to provide a pair of multigrid vacuum tube electrode structures certain of whose electrodes ,are coupled regeneratively and other of whose electrodes function as the load or output circuit.

A more detailed description of the invention follows in conjunction with the drawing, wherein:

Fig. 1 shows one type of known trigger circuit, and

Figs. 2 and 3 show dilIerent embodiments of the electronic trigger circuit of the present invention.

Referring to Fig. 1, there is illustrated a. known type of trigger circuit having one degree of elec trical stability. This trigger circuit comprises a pair of vacuum tubes VI and V2 whose grid and anode electrodes are interconnected to provide a regenerative action. RL2 are connected between the positive terminal +B of a source of anode polarizing potential and the anodes of tubes VI and V2, respectively. The

. anode of tube VI is connected to the grid of tube V2 through a condenser Ch2, while the anode of tube V2 is connected to the grid of tube VI through a resistor-shunt-condenser arrangem'cnt Rhl, ChI. The grid of tube VI is connected to the negative terminal -C of asource of biasingpot'ential through a resistor RdI. The grid of tube V2 is connected to ground through a variable resistor Rd2. Resistors RLI and RL2 might be relatively small compared to the values of the two grid resistors. Normally, in the operation of the trigger circuit of Fig. 1; tube VI is non-conductive and biased to or beyond cut-on by means of source C. Tube V2, however, is

Resistors RLI and normally in a conductive state and passes current because the grid is maintained at substansystem, the trigger will restore itself to the stable state. In order to change the trigger circuit from the stable state'to the active state, it has been customary to apply either a positive pulse to the grid of tube VI or a negative pulse to the grid of tube V2. The positive tripping pulse should be of sumcient magnitude to overcome the negative bias on the grid of tube VI and cause the tube VI to pass current. When tube VI passes current, by virtue of the regenerative action of the circuit, tube V2 will cease conducting, Similarly, if a negative tripping voltage is applied to the grid of tube V2, it should preferably be of suflicient magnitude to bias the tube V2 to cut-off. As a result, due to regenerative action, the tube VI will conduct.

In the circuit of Fig. 2 of the invention, the vacuum tubes comprise pentodes V3 and V4. Each pentode comprises an anode electrode, a suppressor electrode, a screen electrode, a first grid and a cathode. The first grid and the screen electrodes of the two tubes are regeneratively coupled together to form with the cathodes a trigger circuit in substantially the same manner illustrated in Fig. 1. The same reference characters have been employed throughout the fig-- ures in order to represent the same or equivalent elements, The suppressor grid, however, of the normally non-conducting vacuum tube V3 is connected to the cathode of the same tube, while the suppressor grid of the normally conducting vacuum tube V4 is connected to its cathode through its resistor Rt. The screen and anode electrodes of the vacuum tube V3 are individually supplied with positive polarizing potentials from sources +3 and. +BI through resistors RLI and RzI, Similarly, the screen and anode electrodes of tube V4 are individually supplied with positive polarizing potentials from sources +B and +BI through separate resistors RL2 and R22. Sources +3 and +BI may supply either the same or different potentials to the screen and anode electrodes depending upon the values of the circuit elements employed in the trigger circuit. It should be noted that the first. grid of tube V3 is supplied with a negative biasing potential through resistor Rdl to render it normally nonconductlng. It should also 'be noted that the output pulses of either negative or positive relative polarity may be taken from the tubes V3 or V4, respectively, from their anodes by means leads l0 and H. In order to trip the circuit,

it is proposed to supply a negativepulse to the reaching the screen electrode), will trip the circult and cause the normally non-conducting tube V3 to become conducting. This input or tripping pulse applied to the suppressor grid of tube V4 must be relatively large since enough potential must be supplied to reduce the potential between the cathode and screen grid thereof by an amount sumcient to cause triggering. The anodes of the two tubes are electronically coupled to the rest of the tube structures and thus it will be seen that the output circuit is isolated irom the triggering or regenerative circuit and also isolated from the input circuit. In the design 01' the circuit oi Fig. 2, care must be taken to employ the proper values of elements which enter into the regenerative circuit. For example, where direct current anode resistance was employed in the known type of trigger circuit of Fig. 1, we must now employ direct current screen resistance in the embodiment of Fig. 2. etc. The anode resistors Rzl and Rz2 are chosen to best fit the load condition.

Fig. 3 shows a modification of the circuit of Fig. 2, the difference lying primarily in the manner of biasing the tube V3 normally to'current cut-oi! condition. In Fig. 3 there is provided a voltage regulator tube VR between the cathode and ground, and a connection directly fromthe cathode of V3 to the positive source +B through a resistor Rr. The voltage regulator tube VR.

will always be lit and the effect of supplying a positive potential to the cathode is the same as applying a negative potential to the first grid, thus biasing the first grid to the cut-off condition. Putting it in other words, the system of Fig. 3 illustrates an alternative method of biasing the tube V3 to below its cut-oi! potential. Otherwise, the circuit of Fig. 3 functions in substantially the same manner as the circuit of Fig. 2. The average current through the regulator tube VR should not exceed the rated current of this tube, although it can draw greater current than rated for only short intervals. 0! course,

for the same values of +3 and +31, the screen grid and anode potentials of V3 are reduced due to the fact that the cathode is operated at a positive potential.

Although the principles of the invention have been described with reference to a trigger circuit, it will be understood that they are also applicable to a multivlbrator circuit employing pentode vacuum tubes. In utilizing the principles of the invention in connection with a multlvibrator circuit, substantially the same circuit as Fig. 2 can be employed with these exceptions: There will not be used any negative biasing potential for vacuum tube V3, nor will there be used the resistor Rt or the resistor Rhl, or the application of a tripping pulse unless it is desired to simchronize the multivibrator. The suppressor electrode of tube V4 will be connected to its cathode in substantially the same manner as that of tube What is claimed is: 1. A pulse generating trigger circuit comprising first and second pentode vacuum tube electrode structures each having a cathode. a control grid, a screen grid, a suppressor grid and an anode, a condenser coupling the screen grid of said first structure and the control grid of said second structure, a condenser shunted by a resistor coupling the screen grid oi said second structure and the control grid oi said first structure, means for biasingthe control grid of one of said structures to below cut-oil, a direct connection between the suppressor grid and cathode of one oi said structures, a resistor connected between the suppressor grid and cathode oi the other of said structures, means for supplying a tripping pulse of predetermined polarity to the suppressor grid of said last structure, separate resistors connecting said anodes and screen grids to the positive terminal or a source of undirectional potential over separate paths. and an output circuit coupled to an anode oi one of said tubes for deriving an output pulse from said trigger circuit for each application of a tripping input pulse.

2. A self-restoring pulse generating trigger circuit comprising first and second pentode vacuum tubes each having a cathode, a control grid, 9. screen grid, a suppressor and an anode, a condenser coupling the screen grid 0! said first tube and the control grid of said second tube, a condenser shunted by a resistor coupling the screen grid of said second tube and the control grid of said first tube, connections irom each of said cathodes to ground, means for biasing the control grid of said first tube to below cut-ofi, a direct connection between the suppressor grid and cathode of said first tube, a resistor connected between the suppressor grid and cathode of said second tube, separate resistors connecting said anodes and screen grids to the positive terminal of a source or unidirectional potential, whereby said first tube is normally non-conducting and said second tube is normally conducting, means for supplying a tripping pulse of negative polarity to the suppressor grid of said second tube, to thereby reverse the normal current passing states of said tubes, and an output circuit coupled to one or both of said anodes for derivin output pulses from said trigger circuit.

WILLIAM A. MILLER. EUGENE R. snENK.

REFERENCES crr n The following references are of record in the file of this patent:

"Ultra-High Frequency Techniques by Brainerd et a1., 1942, pp. 176-177, published by Van N ostrand. (Copy in Division 51.)

Journal of the Institute of Electrical Engineering, June 1942, Time Bases" by Puckle, p. 110. (Copy in Division 51.)

"Television Synchronizing-Signal Generator, R. C. A. Review, July, 1940.

"Trigger Circuits, Electronics, August, 1939, 

